FIELD OF THE INVENTION
This invention relates to prosthetic terminal devices and more particularly, to a bi-articulated prosthetic terminal device which is characterized by upper and lower proximal jaws that are pivotally joined at a proximal joint for handling large, bulky and/or heavy items and a distal jaw assembly pivotally attached to the upper proximal jaw at a distal joint and fitted with a lower distal jaw which cooperates with the lower proximal jaw, to handle small, light and/or thin items. In a preferred embodiment of the invention, a primary gripping tension or pinch force is provided in the upper proximal jaw and the lower proximal jaw by means of one or more rubber bands or O-rings which encircle the upper proximal jaw and low proximal jaw forwardly of the proximal joint, while a secondary gripping tension or pinch force is provided between the lower distal jaw and the lower proximal jaw by means of a spring located in the distal joint. In another preferred embodiment of the invention, the necessary tension is created in the distal joint by means of a rubber cushion which is seated between the upper distal jaw and the upper proximal jaw.
The bi-articulated prosthetic terminal device of this invention is characterized by the capability for handling both heavy, large and/or bulky items, as well as small, thin and/or light items. This capability is provided in the combination of a curved lower proximal jaw and a curved upper proximal jaw which are pivotally joined at a proximal joint and tensioned by one or more rubber bands or O-rings, in combination with a secondary, V-shaped distal jaw assembly which is pivotally attached to the upper proximal jaw. The bi-articulated prosthetic terminal device of this invention can be activated by conventional body-powered or externally-powered means and installation may be effected by standard connections such as the one-half-inch by twenty-inch threaded stud-to-wrist unit or by mounted bearing and friction ring-to-laminating ring connections which are well known to those skilled in the art. External power may be supplied by hydraulics and pneumatic systems, as well as electricity, in non-exclusive particular. Furthermore, due to the unique design of the bi-articulated prosthetic terminal device of this invention, the pinch force and the energy expenditure required for activation of this pinch force may be selected. Currently, the same energy is required to activate a conventional prosthetic terminal device, regardless of whether the object being acted on requires a greater or smaller pinch force for manipulation. Using the bi-articulated terminal device of this invention, very small, thin and/or light items may be grasped at the distal tip of the device by pivoting the distal joint assembly only, with the expenditure of much less energy than is necessary to activate the interior, primary proximal jaws. Accordingly, the bi-articulated prosthetic terminal device of this invention causes the "body powered" wearer less muscle and joint fatigue and also effects less battery drainage for the "externally powered" user.
Due to the nature of the control cable and harness elements of a terminal prosthetic device, the pinch force pressure in the device itself is directly proportional to sound side axilla pressure at the point of harness contact. Using the bi-articulated terminal device detailed herein, full operating pressure would be applied only when maximum pinch force is required, as described above, rather than indiscriminately, only for the purpose of opening the prosthetic terminal device. Furthermore, because of the progressive application of tension required to operate a conventional prosthetic terminal device through its full range of motion, either by external battery operation or by body power, an exceptionally smooth action is generated using the bi-articulated terminal device of this invention. This is due to the pre-loading effect of the light spring or the rubber cushion located in the distal jaw assembly, which pre-loading is necessary prior to operating the distal jaw assembly, where the heavier rubber band or O-ring which operates the upper and lower proximal jaws is stretched open. Not only is this arrangement considered to be easier on conventional gear trains and motors of externally-powered prosthetic terminal devices, but it also affords the body-powered wearer a smoother, less deliberate appearance when activating his or her bi-articulated prosthetic terminal device.